printf脚本中的格式问题

Question

I have a file stv.txt containing some names
For example stv.txt is as follows:

hello  
world  

I want to generate another file by using these names and adding some extra text to them.I have written a script as follows

for i in `cat stvv.txt`; 
do printf 'if(!strcmp("$i",optarg))' > my_file; 
done

output

if(!strcmp("$i",optarg))  

desired output

if(!strcmp("hello",optarg))  
if(!strcmp("world",optarg))

how can I get the correct result?

Answer 1

This is a working solution.

1 All symbols inside single quotes is considered a string.
2 When using printf, do not surround the variable with quotes. (in this example)

The code below should fix it,

for i in `cat stvv.txt`; 
   printf 'if(!strcmp('$i',optarg))' > my_file; 
done

basically, break the printf statement into three parts.

1: the string 'if(!strcmp('
2: $i (no quotes)
3: the string ',optarg))'

hope that helps!

Answer 2

To insert a string into a printf format, use %s in the format string:

$ for line in $(cat stvv.txt); do printf 'if(!strcmp("%s",optarg))\n' "$line"; done
if(!strcmp("hello",optarg))
if(!strcmp("world",optarg))

The code $(cat stvv.txt) will perform word splitting and pathname expansion on the contents of stvv.txt . You probably don't want that. It is generally safer to use a while read ... done <stvv.txt loop such as this one:

$ while read -r line; do printf 'if(!strcmp("%s",optarg))\n' "$line"; done <stvv.txt
if(!strcmp("hello",optarg))
if(!strcmp("world",optarg))

Aside on cat

If you are using bash , then $(cat stvv.txt) could be replaced with the more efficient $(<stvv.txt) . This question, however, is tagged shell not bash . The cat form is POSIX and therefore portable to all POSIX shells while the bash form is not.